Direct ab initio dynamics studies of the hydrogen abstraction reactions ofhydrogen atom with fluoromethanes

A direct ab initio dynamics study on the gas-phase reactions of atomic hydr ogen with different fluoromethanes has been carried out. The thermal rate c onstants were calculated using canonical variational transition state (CVT) theory augmented by multidimensional semiclassical zero and small curvatur e tunneling approximations. The potential energy surfaces for the reactions were calculated using hybrid density functional theory, namely, Becke's ha lf-and-half (BH) nonlocal exchange and the Lee-Yang-Parr (LYP) nonlocal cor relation functionals using the cc-pVDZ basis set. The reaction energies and barrier heights were improved by single-point energy calculations along th e minimum energy path (MEP) at the spin-projected fourth order Moller-Pless et perturbation theory (PMP4) using the cc-pVTZ basis set. The calculated f orward and reverse thermal rate constants are in the good agreement with th e experimental data. The electronic effects of fluorine substitution on the rate of this class of reactions are examined.